Electrosurgical instruments for delivering radio frequency (RF) electrical energy into solid tissue are known. For example, published PCT application WO 96/29946 discloses electrosurgical probes that include a number of independent wire electrodes that may be extended into tissue from the distal end of a cannula. The electrodes may be energized in a monopolar or bipolar manner to heat and necrose a target tissue region. Such probes have been suggested for treating tumors within organs, such as the liver, kidney, pancreas, stomach, and spleen.
To enhance heating and necrosis, saline may be injected into the target region before delivering electrical energy. Generally, this involves advancing a needle from a syringe into the tissue before or after advancing the electrodes from an electrosurgical probe into the target region. Saline may be delivered from the syringe into the tissue through the needle, and then the electrodes may be energized to deliver RF energy and necrose tissue within the target region. Alternatively, saline may be delivered through a lumen in one or more of the wire electrodes. Saline may increase heating of the tissue, thereby increasing the size of the resulting lesion, as compared to energizing the electrodes without saline.
Because of inhomogeneities in the tissue of the target region, however, the saline injected by the syringe may not be perfused into the target region in a desired manner. For example, the saline may be perfused into tissue away from the electrodes, or only locally within a portion of the target region. Thus, the tissue within the target region may not be uniformly heated and necrosed as desired, possible requiring multiple treatments to ensure that the target region is successfully necrosed. In addition, where a separate syringe is used to deliver the saline, the syringe and probe require separate approaches into the tissue, complicating access and creating multiple tracks through the intervening tissue that may need to be closed and allowed to heal.